Assessment of Plasma Resistivity as a Surrogate for Extracellular Fluid Resistivity: Analytical Performance and Impact of Fluid Composition.
basic_science · Level V
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- Record sourced from PubMed, PMID 30891658.
- Also identified by DOI 10.1007/s10439-019-02246-9.
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Abstract
Bio-electrical impedance analysis (BIA) is frequently used to assess body composition in man. Its accuracy in patients is limited, possibly because the employed algorithms are based on the assumption that total body electrical resistance (TBER) is exclusively related to body water volume, and that variation in fluid composition and its effect on fluid resistivity can be ignored. This may introduce substantial calculation errors. The aim of this study was to develop an objective method to assess plasma resistivity (ρ<sub>plasma</sub>) based on measurements by a conductivity probe, as a surrogate for extracellular fluid resistivity (ρ<sub>e</sub>). Sample measurements were standardized at body temperature. Analytical variation was 0.6% within runs and 0.9% between runs. The critical difference, i.e. the smallest difference needed to consider changes within individuals significant, was 1.8% for measurements within runs and 4.3% for measurements between runs. The normal range was defined by a mean ± SD of 66.9 ± 1.8 Ω cm. Multiple regression demonstrated that ρ<sub>plasma</sub> was inversely related to plasma sodium and chloride concentrations, and positively related to total protein (overall R<sup>2</sup> = 0.92, p < 0.001). In conclusion, ρ<sub>plasma</sub> measurements were sufficiently robust to be useful as a tool to examine and improve the validity of BIA in clinical settings.
Medical subject headings
- Electric Impedance
- Plasma